Description:

Objective:

This project explores the efficacy of using CNTs as catalysts for advanced oxidation processes (AOPs), targeting the removal of pharmaceuticals and pharmaceutically active compounds (PhACs) during wastewater treatment. Catalytic ozonation research using activated carbon (AC) to enhance hydroxyl radical production via ozone decomposition suggests that AC high in surface area and exhibiting basic surface functionalities is most effective. Due to the higher surface area and unique material and surface properties of CNTs relative to AC, it is expected that CNT-catalyzed ozonation will show improved removal of PhACs across a broad range of structurally diverse organic micropollutants and will achieve a higher degree of mineralization, compared with traditional AOPs.

Synopsis:

Pharmaceuticals and related compounds (PhACs) have been found in surface- and drinking-water systems throughout the United States. The main entry route for PhACs into these water systems is wastewater treatment plant (WWTP) effluent. Current research suggests that the impact of WWTP discharges on human and ecosystem health may be far greater than is now understood. This project explores the use of carbon nanotubes (CNTs) as catalysts for advanced oxidation to improve removal of PhACs during wastewater treatment.

Approach:

This study includes two phases: synthesis and characterization of functionalized CNTs; and, reactivity and performance assessment of synthesized materials. Phase One involves development and characterization of a collection of CNTs with distinct surface chemistries. Specific tasks include both covalent and non-covalent surface functionalization of CNTs. All tasks will use commercially available single-walled (SW), double-walled (DW), and/or multi-walled (MW) CNTs. Phase Two will use materials synthesized in Phase One to determine their efficacy in hydroxyl radical generation during ozonation. These data, coupled with the characterization data compiled in Phase One, will yield a greater understanding of the CNT-surface properties affecting catalytic ozonation. A second goal of Phase Two is to determine how variations in water chemistry and composition influence the operational performance of these catalysts during treatment applications. This phase looks first at CNT performance in model water systems; the most promising catalysts will then undergo further performance testing in variable water quality systems.

Expected Results:

Preliminary results suggest that CNTs enhance ozone decomposition and that the rate of this reaction is tunable through CNT functionalization. Using chemical probe compounds, enhanced hydroxyl radical production has been observed at CNTs loading as low as 5 mg/L, compared with 500 mg/L of AC required to achieve a noticeable increase in ozone decomposition. Further, preliminary results show that greater hydroxyl radical production in the CNT-catalyzed system results in greater PhAC removal than with either ozone or CNTs alone. These results support the hypothesis that CNT-catalyzed ozonation offers promise for use in advanced water and wastewater treatment for increased removal of emerging organic micropollutants, including PhACs.

Potential to Further Environmental/Human Health Protection:

A key outcome of this research is development of new technologies to promote sustainable water reuse. As more and more communities search for ways to make better use of their resources to meet drinking water needs, effective treatment of wastewater will become increasingly important. CNTs can be a valuable tool in reducing PhACs from wastewater effluent; it is foreseeable that CNT-catalyzed ozonation technologies may simultaneously disinfect the wastewater, break down PhACs and other micropollutants, and minimize or sequester ozonation byproducts, thereby offering promise for improved protection of human health and the environment.

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.